Generate the C main() function when linking a binary (fixes #5373)

Rather than have main() be statically compiled as part of the RTS, we
now generate it into the tiny C file that we compile when linking a
binary.

The main motivation is that we want to pass the settings for the
-rtsotps and -with-rtsopts flags into the RTS, rather than relying on
fragile linking semantics to override the defaults, which don't work
with DLLs on Windows (#5373).  In order to do this, we need to extend
the API for initialising the RTS, so now we have:

void hs_init_ghc (int *argc, char **argv[],   // program arguments
                  RtsConfig rts_config);      // RTS configuration

hs_init_ghc() can optionally be used instead of hs_init(), and allows
passing in configuration options for the RTS.  RtsConfig is a struct,
which currently has two fields:

typedef struct {
    RtsOptsEnabledEnum rts_opts_enabled;
    const char *rts_opts;
} RtsConfig;

but might have more in the future.  There is a default value for the
struct, defaultRtsConfig, the idea being that you start with this and
override individual fields as necessary.

In fact, main() was in a separate static library, libHSrtsmain.a.
That's now gone.

1 files changed, 3 insertions, 1 deletions

diff --git a/rts/RtsFlags.h b/rts/RtsFlags.h
index a6bfe0a924..73eb6688a6 100644
--- a/rts/RtsFlags.h
+++ b/rts/RtsFlags.h
@@ -15,7 +15,9 @@
 /* Routines that operate-on/to-do-with RTS flags: */
 
 void initRtsFlagsDefaults (void);
-void setupRtsFlags        (int *argc, char *argv[]);
+void setupRtsFlags        (int *argc, char *argv[],
+                           RtsOptsEnabledEnum rtsOptsEnabled,
+                           const char *ghc_rts_opts);
 void setProgName          (char *argv[]);
 void freeRtsArgs          (void);